The present invention relates to a negative temperature coefficient (i.e. "N.T.C.") thermistor for use in temperature measurement, control, and compensation of electronic elements or circuits.
A typical N.T.C. thermistor is shown in U.S. Pat. No. 4,786,888. This patent discloses a thermistor element produced through sintering ceramic in the form of a chip. It is sandwiched by a pair of electrodes and enclosed in an envelope made of glass. In this regard, the device only operates to secure or stabilize the thermal or chemical properties of the thermistor element when the thermistor is used for measuring temperature.
A thermistor of the above type has many drawbacks requiring relatively complex production processes, low production capacities, poor yields, and unnecessary diffusive boundary layers. In addition, such thermistor elements require leads which require connections to external devices. This makes difficult the assembly of the thermistor element onto a circuit board.
A less difficult way to build a surface mounted thermistor element which would secure the thermal, chemical and solderability properties would be enveloping the thermistor element in a low K dielectric material. The letter "K" designates the dielectric constant of the material, and a low constant dielectric material reduces capacitance with respect to related conductors. This low K dielectric material, which is low fire and acid resistant, would accept silver electrodes that are compatible with nickel, and Sn/Pb plating. This eliminates the need for complex production processes, poor yields, and unnecessary diffusive boundary layers.
Therefore, a principal object of this invention is to provide a surface mount thermistor element that would maintain thermal, chemical, and solderability properties, and which is more reliable.
A further object of this invention is to provide a method of making a thermistor which is economical and efficient, and which will not be detrimental to the resulting product.
A further object of the present invention is to provide a negative temperature coefficient ceramic material that can be plated with nickel and tin (Sn)./lead (Pb) plating for surface mount applications.
A still further object of this invention is to provide a negative temperature coefficient thermistor with production processing steps which has an envelope of low K insulating dielectric for enclosing the thermistor for surface mount applications.
A still further object of the present invention is to provide a thermistor of the above type suitable for soldering directly onto a printed circuit board for surface mount applications.
A still further object of the present invention is to provide a thermistor which is stable in operation at higher operating temperatures for surface mount applications.
A still further object of the present invention is to provide a method of producing thermistors in high volumes and with excellent yields.
These and other objects will be apparent to those skilled in the art.